The present invention relates to a particle detector and particle detecting apparatus having the detector for detecting and analyzing particles by passing particles of cells, blood corpuscles or the like through an orifice in a sheath flow.
A particle detecting apparatus disposing a pair of electrodes across an orifice (aperture) for detecting particles individually on the basis of changes of electric impedance caused when particles pass through the orifice is known well. Also known well is a particle detecting apparatus for forming a sheath flow, and passing the particles in neat order in the center of its orifice. In this case the term "sheath flow" means a flow of a suspension of particles of which surrounded an covered by a laminar flow liquid (sheath liquid), in order to pass particles precisely and neatly in one row in the middle of the orifice.
In such a particle detecting apparatus, the inside diameter of the orifice is, as a matter of course, unchanged, and the size of measurable particles is limited. For example, when measuring large particles, problems of clogging or loss of linearity (linear correlation) occur between the size of particles and magnitude of detection signal, or when measuring small particles, a sufficient S/N ratio is not obtained, and signals are concealed by noise and cannot be detected. By raising the detection current, the S/N ratio may be raised somewhat, but it may result in adverse effects on particles or lead to other problems. The S/N ratio is the ratio of the desired signal to the noise mixed in the signal, and the higher the S/N ratio, the easier it is to detect signals.
The measure from small particles without problems to large particles, it is necessary to vary the size of the orifice depending on the particle size. That is, in the case of large particles, it is necessary to measure with a wider orifice diameter, and in the case of small particles, a narrower orifice diameter is desired. However, since the orifice is assembled into the detector in one body, to vary the orifice diameter, it is necessary to prepare a plurality of detectors having different orifice diameters, and exchange the detector in assembly depending on the particles to be measured.
If the diameter of the orifice is variable, the measuring range of particles may be extended. In the conventional apparatus, this took time because the detectors were exchanged. Further, the orifice diameter could not be varied freely. If the orifice diameter is freely variable, it may be possible to measure particles of any size under optimum conditions, which represents a great progress for in particle measurement.